1. Field of the Invention
The present invention relates to a link plate for silent chains and a method of producing the link plate.
2. Description of the Related Art
A silent chain which is used as a timing chain for an engine, a power drive chain for a transmission and so on includes a large number of link plates articulately connected together in an endless fashion by means of pins with the link plates being interleaved in transverse and longitudinal directions of the chain. Each of the link plates has a pair of link teeth designed to engage or mesh with teeth of a sprocket at inner flanks or outer flanks thereof for achieving power transmitting operation.
The conventional silent chain is generally manufactured in the manner as described below: A coiled sheet metal while being unwound is fed longitudinally through successive working positions. While the sheet metal is at rest at a first working position, a pair of pin holes is formed in the sheet metal by means of a punch, and at a second or next subsequent working position, a link plate is blanked out from the sheet metal by means of a blanking punch. In another conventional manufacturing process, a link plate blank having substantially the same outline as a finished link plate is blanked out from sheet metal, and subsequently a pair of pin holes is punched in the link plate blank, thereby producing a link plate. A number of such link plates are articulately connected together by means of pins so as to form an elongated chain with the link plates being interlaced with each other in both transverse and longitudinal direction of the chain. Thereafter, the elongated chain of link plates is cut off into desired lengths which are determined according to the application or use of a finished silent chain. The link plates at opposite ends (a leading end and a trailing end) of the desired length of chain are then abutted together in an intermeshing fashion and joined together by a pin, thus forming an endless chain.
In order to facilitate easy intermeshing between the link plates at the leading and trailing ends of the desired length of chain, and also to obtain flat link plates free from local wear, a burring process or a grinding process is carried out during the manufacture of the link plates in such a manner that the circumferential edges of the link plates are uniformly chamfered or rounded throughout the length thereof into beveled or rounded surfaces.
However, the aforementioned link plate matching process is usually achieved by manual operation and difficult to automate because it involves an alignment for bringing together two groups of laterally spaced link plates into intermeshed condition at the leading and trailing ends of the desired length of chain.
To facilitate easy matching of the link plates, it becomes necessary to make a chamfer on a matching part of the link plate as large as possible. There arises a problem however that the burring or grinding process requires a long working time for providing such large chamfering. This reduces productivity and also results in deterioration of the fatigue strength of the link plates.
In addition, since an unnecessary part of the circumferential edge of each link plate, that is, an engagement surface on each link tooth of the link plate is also chamfered greatly, engagement surfaces on the link teeth of the link plate are narrowed. When used with a sprocket, the link plate having such narrowed engagement surfaces exerts a great pressure or force on a toothed surface of the sprocket, tending to produce abnormal wear on the toothed surface of the sprocket.
With the foregoing drawbacks of the prior art in view, it is an object of the present invention to provide a link plate for silent chains which is capable of being smoothly matched or intermeshed with similar link chains when opposite ends of an elongated chain are abutted together to form an endless chain, which enables automated assembly of the chain, and which is capable of reducing wear on the toothed surface of a sprocket.
Another object of the present invention is to provide a method of producing such link plate which can reduce the necessary working time of the burring or a grinding process, thereby increasing productivity.
According to a first aspect of the present invention, there is provided a link plate for a silent chain, having a pair of pin holes formed therein, a pair of link teeth on one side thereof extending in a longitudinal direction of the chain, and a butt-inserting portion formed at at least one of opposite ends thereof in the longitudinal direction of the chain, wherein the butt-inserting portion has a thickness decreasing gradually toward a circumferential edge of the link plate at said at least one end of the link plate.
For making a silent chain, a plurality of such link plates are articulately connected together by means of pins so as to form an elongated chain in which the link plates are interleaved in both a transverse direction and a longitudinal direction of the chain. Then, opposite ends of the elongated chain are joined together by a pin in which instance by virtue of the butt-inserting portions, the link plates at the opposite chain ends can be smoothly intermeshed with each other. This is because the butt-inserting portion is tapered and hence it can provides a clearance between one link plate at one end of the elongated chain and an adjacent link plate at the other end of the elongated chain when the two link plates are brought or abutted together from opposite directions into a laterally juxtaposed condition. By thus provided clearance, the two link plates can be smoothly brought together into such laterally juxtaposed condition without interference even when the directions of movement of the two plates being abutted are misaligned to some extent.
In one preferred form, the butt-inserting portion of the link plate is comprised of a beveled surface formed on at least a front surface or a rear surface of the link plate. The butt-inserting portion may be provided at the opposite ends of the link plate and comprised of a beveled surface formed on the front and rear surfaces of the link plate. The beveled surface preferably has a generally fan shape with its pivot located at the circumferential edge of the link plate at each end of the link plate.
In another preferred form, the circumferential edge on at least one of a front surface and a rear surface is beveled to a greater extent at said at least one end of the link plate than at a remaining portion of the link plate including the link teeth. The butt-inserting portion includes such beveled circumferential edge of the link plate at said at least one end of the link plate. The beveled circumferential edge preferably has a generally fan shape with its pivot located at the circumferential edge of the link plate at said at least one end of the link plate.
According to another aspect of the present invention, there is provided a method for producing a link plate for a silent chain, the link plate having a pair of pin holes formed therein, a pair of link teeth on one side thereof extending in a longitudinal direction of the chain, and a butt-inserting portion formed at at least one of opposite ends thereof in the longitudinal direction of the chain, the butt-inserting portion having a thickness decreasing gradually toward a circumferential edge of the link plate at said at least one end of the link plate. The method comprises the steps of: feeding a coiled sheet metal intermittently along a path while unwinding the coiled sheet metal; in synchronism with the intermittent feed of the sheet metal, depressing the sheet metal from at least one side thereof so as to form a depressed portion in at least one of a front surface and a rear surface of the sheet metal, the depressed portion having a sloped bottom surface facing in one direction for forming a butt-inserting portion of a link plate to be produced; in synchronism with the intermittent feed of the sheet metal, punching a pair of pin holes in the sheet metal at respective positions predetermined with respect to the depressed portion; and thereafter, in synchronism with intermittent feed of the sheet metal, die-cutting a link plate out from the sheet metal while using the pin holes as a reference position so that a circumferential edge of the die-cut link plate extends across the depressed portion to thereby form a butt-inserting portion.
The depressing may be achieved such that two depressed portions are formed in a spaced relation in the front surface or the rear surface of the sheet metal. As an alternative, the depressing may be effected from opposite sides of the sheet metal so that the depressed portion is formed in both the front surface and the rear surface of the sheet metal. Preferably, the depressing is effected from opposite sides of the sheet metal such that two depressed portion are formed in a spaced relation in the front and rear surfaces of the sheet metal.
In order to remove a shear drop and a roughened surface which may be produced as a result of the punching and die-cutting processes, inner circumferential surfaces of the punched pin holes and an outer circumferential surface of the link plate may be finished by shaving with suitable shaving tools. The finished or shaved circumferential surfaces have an improved degree of surface roughness and high surface qualities including parallelism.